In the field of vehicle design, there continues to be increased emphasis on vehicle light-weighting. Advantages of light-weighting include improved fuel economy and reduced materials costing. As a result of this increased emphasis on vehicle light-weighting, many vehicle parts and components traditionally made of steel are presently being replaced with other materials, such as aluminum and plastic. One example part of this type is the spare tire well or pan, particularly that used in sedan-type vehicles, which is often disposed in the trunk of the vehicle. Previously, the spare tire pan was made of stamped sheet metal and attached to the vehicle white body by means of welding. There is now interest in manufacturing the spare tire pan of a lighter material.
Attaching non-steel parts (e.g., resin parts) to a vehicle body can present numerous technical challenges as compared to traditional fastening methods for metal-to-metal connections. While mechanical attachments such as bolts, screws, rivets, etc. are possible, these methods present unique challenges for resin parts in terms of long term durability of the attachment, particularly due to concerns from heating and continuous loading. If not carefully engineered, there is a potential for such conditions to cause premature failure of the connections due to torque loss from creep in the plastic material. Such concerns can be reduced by using metal collars inserted into the fastener area of the plastic to ensure metal-to-metal contact between the fastener and the vehicle body, but use of such metal collars increase costs.
Another alternative fastening method involves the use of adhesives to bond a plastic part to a metal structure. With proper surface treatment of the bonded surfaces, this technique can be very effective in achieving a high quality, durable bond. One drawback of this technique, however, is the length of time it typically takes for the bond between the two materials to cure or “set up.” In other words, sufficient time must be given for the adhesive to cure and the bond to become established. During this period, there is a need to limit any relative motion between the surfaces to be bonded. In vehicle manufacture, this is often not feasible because the vehicle is moved along an assembly line and is subject to jostling. To stop movement of a vehicle body along an assembly line for the amount of time required to set up such a bond would reduce efficiency of the manufacturing line undesirably.